The present invention is particularly suited for use with tie-down systems used to anchor wood-framed buildings to their foundations. Many such systems use a rod or bolt that is anchored at its lower end to either a lower member of the building or directly to its foundation. The upper end of the bolt or rod is connected to a plate or bracket which, in turn, is connected to an upper portion of the building. The rod or bolt is usually connected to the bracket by means of a nut thread onto the bolt or rod that presses against the plate or bracket. The rod or bolt is placed in tension by tightening the nut against the plate or bracket that receives the rod or bolt.
For the rod or bolt to serve as an effective anchor for the building it is important that the rod remain in tension and, correspondingly, that the nut continue to compress the plate or bracket. However, a number of different factors can cause the nut to move away from the bolt, which causes the rod to lose its tension.
One such factor is wood shrinkage. Most lumber used in wood-frame construction has a relatively high water content when the building is constructed. However, once the envelope of the building is completed, the lumber is no longer exposed to the relatively humid outside air, and it begins to lose moisture which leads to shrinkage. A standard 2×4 can shrink by as much as 1/16″ of an inch across its grain within the first two years that it is incorporated in a building.
A wide variety of methods have been proposed to maintain the tension in anchoring rods and bolts used in tie down systems for buildings. See, for example: U.S. Pat. No. 5,180,268, granted to Arthur B. Richardson on Jan. 12, 1993; U.S. Pat. No. 5,364,214, granted to Scott Fazekas on Nov. 15, 1994; or U.S. Pat. No. 5,522,688, granted to Carter K. Reh on Jun. 4, 1996. These devices are interposed between two work members and expand as the two members separate, maintaining the connection or contact between them. These devices are designed to expand without reversing or contracting once they are installed.
U.S. Pat. No. 5,081,811, granted to Kensuke Sasaki on Jan. 21, 1992 (Sasaki '811) takes a different approach. Sasaki '811 uses a special one-way sliding nut that is attached to the wood member upon which it bears. As the building shrinks or settles, the Sasaki nut travels with the building down on the rod by means of its one-way sliding feature.
Another approach is taught by U.S. Pat. No. 4,812,096. This patent was granted to Peter O. Peterson on Mar. 14, 1989. In this method, the tension rods are pulled into connecting brackets as the building shrinks and settles, such that the over-all length of the tie-down system is reduced.
The present invention represents an improvement over the prior art methods. The present invention provides a novel expansion device that is fully adjustable, has protective members for shielding the working mechanisms of the device from the elements and dirt and grime, provides a rigid force transmitting mechanism, and has built in redundancy in the expansion mechanism so that the device is less likely to fail.